1. Field of the Invention
The present invention relates to torque sensitive clutch assemblies for use with V belts, which also may include speed sensitive means.
2. Prior Art
In the prior art various V belt clutches that are both speed and torque sensitive have been advanced. For example, U.S. Pat. No. 3,868,862 shows an expansible pulley having both speed and torque sensitive means thereon, and includes linkages that can be changed in position so that the torque sensitive means may either be added to or subtracted from the force of the centrifugal weights. That is, in this particular device the drive to the movable pulley half is through adjustable links and in one position, the links will tend to move the movable pulley half into a lower drive ratio under increasing load, and in another position will tend to move the pulley into a higher drive ratio with increasing load. However, in this patent, it appears that the links used for accomplishing this end may not have sufficient durability for extended use at high power transmission levels, nor under conditions where the pulley is changing frequently and rapidly. Costs of manufacture and assembly also appear to be high.
U.S. Pat. No. 3,395,587 shows a torque sensitive stepless speed change drive using a somewhat different principle, but providing a torque sensitive reaction, once a preset spring force is exceeded, that will cause the drive ratio to decrease as the torque or load on the clutch increases. A much different mechanism is utilized in this device.
In addition, applicant is aware of U.S. Pat. No. 3,996,811 which shows a combined speed and torque sensitive clutch, wherein the speed sensitive portions of the clutch are the same as that shown herein, but where the torque sensitive means includes facing, end engaging cam surfaces between the movable sheave and stationary portions of the clutch.
The inventor is further aware of a clutch similar to that shown in U.S. Pat. No. 3,968,702 where the cam lowers the drive ratio under load as with the present device but wherein wide spiral grooves were formed in a ring on the stationary member which partially surrounded the hub of the movable sheave portion, and short ribs adjacent the end of the movable sheave rode in the grooves. One problem with the described modified clutch was that the grooves had to be formed in the ring of the stationary member at a "negative rake angle" when viewed from the open end of the ring. This made it extremely difficult to fabricate, and required machining for forming the grooves.
Another patent of interest is French Pat. No. 1,148,087 which shows a speed and torque sensitive device.